Device for extracorporeal blood treatment having an evaluation and control unit

ABSTRACT

The invention relates to a blood treatment device having an extracorporeal blood circuit which comprises an arterial line, a blood pump, a blood treatment unit and a venous line, wherein the arterial and venous lines can be connected to a blood vessel of a patient, and wherein the blood treatment device has an evaluation and control unit, wherein the evaluation and control unit is configured to carry out the following steps: (a1) determining the blood recirculation in a blood vessel of the patient connected to the extracorporeal blood circuit; and (b) calculating the blood flow in the blood vessel using the blood recirculation determined in accordance with (a1) and using a provided value or a value likewise previously determined for the cardiac output of the patient.

The invention relates to a blood treatment device having anextracorporeal blood circuit which comprises an arterial line, a bloodpump, a blood treatment unit and a venous line, wherein the arterial andvenous lines can be connected to a blood vessel of a patient, andwherein the blood treatment device has an evaluation and control unitfor determining the blood flow in the involved vessel of the patient.

The requirement for an efficient extracorporeal blood treatment, forexample efficient dialysis, is the presence of a working vessel access.

An arteriovenous fistula is therefore frequently artificiallyestablished for the extracorporeal blood treatment, typically in thelower arm between the radial artery and the cephalic vein. The vesselpressure is increased by this short-circuiting of the artery and vein;it is caused by a reduced tissue resistance. A high blood flow in theinvolved vessel is thus achieved.

In order moreover to ensure a working vessel access, different methodsare recommended in the relevant guidelines. They include the measurementof the recirculation on the removal from the vessel access and thedetermination of the flow in the vessel access such as is known fromSchneditz et al. (1998): “measurement of access flow during hemodialysisusing the constant infusion approach”, ASAIO Journal 44, p. 74ﬀ.However, only a very rough evaluation of the vessel access can be madeon the basis of recirculation values. The measurement of the flow in thevessel access requires a temporary swapping over of the arterial andvenous needles and a special disposable and actions of the user arerequired for this.

It is, for example, known in the prior art from WO 2011/131358 A2 todetermine the fistula blood flow on the basis of dilution measurements.The patents EP 0 773 035 B2 and EP 1 576 341 B1 also deal with thesubject of determining the fistula blood flow.

It is an object of the invention to provide a device for extracorporealblood treatment which allows a simple and reliable measurement of theblood flow in the vessel access.

Against this background, the invention relates to a blood treatmentdevice having an extracorporeal blood circuit which comprises anarterial line, a blood pump, a blood treatment unit and a venous line,wherein the arterial and venous lines can be connected to a blood vesselof a patient, and wherein the blood treatment device has an evaluationand control unit. In accordance with the invention, the blood treatmentdevice is characterized in that the evaluation and control unit isconfigured to carry out the following steps: (a1) determining the bloodrecirculation in a blood vessel of the patient connected to theextracorporeal blood circuit; and (b) calculating the blood flow in theblood vessel using the blood recirculation determined in accordance with(a1) and using a provided value or a value likewise previouslydetermined for the cardiac output of the patient.

The blood treatment device can, for example, be a dialysis machine or anapheresis machine. The blood treatment unit can, for example, be adialyzer or a plasma filter.

In an embodiment, the blood treatment device furthermore has a bloodpressure sensor and the evaluation and control unit is configuredfurthermore to carry out the following step prior to step (b): (a2)determining the cardiac output of the patient by evaluating the timeprogression of a pressure pulse measured using the blood pressuresensor. The blood pressure sensor can furthermore be suitable to measurethe blood pressure directly at the patient, for example at the patient'sarm or wrist. Suitable pressure sensors comprise piezoelectric pressuresensors.

Provision can therefore be made within the framework of the inventionthat the cardiac output is determined from oscillometric blood pressuremeasurements. The evaluation of such oscillometric blood pressuremeasurements is known, for example, for determining the blood pressure(cf. DE 10 2012 007 081 A1).

Methods based on pulse analysis for determining the cardiac output areknown in the prior art. All these methods use pulse curves to determinethe cardiac output. The evaluation and control unit of the bloodtreatment device in accordance with the invention can be configured todetermine the cardiac output using such a method based on pulse analysisand then to use it in step (b).

Suitable methods based on pulse analysis comprise the impulse responsemethod, which is described in more detail, for example, in US2011/0034813 A1, or the model flow method which is described in moredetail in EP 0 569 506 B1.

The determination of the cardiac output from the mean arterial bloodpressure, the central nervous pressure and the peripheral resistance ispreferred such as is used in the commercially available “Vicorder”device of the company SMT medical GmbH.

In an embodiment, the blood treatment device furthermore has a bolussensor arranged in the arterial line of the extracorporeal blood circuitand the evaluation and control unit is configured to carry out step (a1)in the following manner: (a1) determining the blood recirculation in ablood vessel of the patient connected to the extracorporeal bloodcircuit using the signal of the bolus sensor.

In an embodiment, the blood treatment device has a control unit and anactuator, wherein the actuator is configured such that a bolusadministration can take place downstream of a blood pump arranged in theextracorporeal blood circuit and/or downstream of the blood treatmentunit, and wherein the control unit is configured such that a bolusadministration takes place once or a plurality of times when using theactuator during a measurement interval. The actuator can, for example,be a heating with which a temperature bolus can be produced. Theactuator can furthermore be a metering system which opens into theextracorporeal blood circuit and with which a concentration bolus ortemperature bolus can be produced.

The blood treatment device furthermore preferably has a bolus sensorarranged in the venous line of the extracorporeal blood circuit, whereinthe evaluation and control unit is configured to determine the bloodrecirculation in the vessel section of the patient while using thesignals of the arterial and venous bolus sensor. Provision can inparticular be made that the evaluation and control unit in this respecttakes account of the similarity of the signal progressions and the timeoffset of the signals obtained from the different sensors.

The bolus sensor or sensors can be temperature sensors to recognize atemperature bolus.

The measurement of the recirculation between the venous and arterialneedles by means of thermodilution is described, for example, inSchneditz et al. (2003), “Surveillance of Access Function by the BloodTemperature Monitor”, Seminars in Dialysis 16, p. 483ﬀ. In this respect,a temperature bolus is produced at the blood side downstream of thedialyzer and is detected by a sensor system at the venous and arterialhose systems. The recirculation is calculated by the comparison of thetemperature boli measured at the venous and arterial sides. Thespecified measurement accuracy amounts to ±2%. The interpretation of thevalues takes place without considering vital parameters of the patientor treatment parameters. Values <10% are thus generally considered as anormal cardiopulmonary recirculation, whereas larger values areevaluated as indications of the presence of recirculation in the vesselaccess, e.g. due to a swapping over of the arterial and venous needles.

In an embodiment, the evaluation and control unit is configuredfurthermore to take account of the extracorporeal blood flow and theoutflow of fluid in the blood treatment device, in addition to the bloodrecirculation and the cardiac output, when determining the blood flow instep (b). The extracorporeal blood flow Q_(b) can be set, for example,by setting the conveying rate of a blood pump present in the arterialline. The outflow of fluid in the blood treatment device can inparticular be the ultrafiltration rate. It can be set, for example,using a UF pump which is arranged in a dialysis fluid system likewiseconnected to the dialyzer.

In an embodiment, the evaluation and control unit is configured todefine critical values for the recirculation for a normal and/or inverseconnection of the arterial and venous lines to the blood vessel underthe assumption that the blood flow in the corresponding vessel canachieve a specific portion of the cardiac output as a maximum. Themaximum portion in the cardiac output which the blood flow can reach asa maximum in the corresponding vessel can be 50%, for example. Criticalvalues for the recirculation can thus be defined at normal and inverseneedle positions. The critical values differ depending on the flow inthe extracorporeal blood circuit.

In an embodiment, the evaluation and control unit is configured tocompare the determined recirculation with these critical values and togroup them on the basis of the comparison.

In an embodiment, the device furthermore has an output unit whichcommunicates with the evaluation and control unit, wherein the outputunit and the evaluation and control unit are configured to output adifferent signal to the user depending on the group association of thedetermined recirculation. The output unit can, for example, outputacoustic and/or visual signals to the user.

In an embodiment, three groups are distinguished: (1) the determinedrecirculation is below the critical values for a normal connection; (2)the determined recirculation is above the critical values for a normalconnection, but below the critical value for an inverse connection; and(3) the determined recirculation is above the critical value for aninverse connection.

With respect to the signal output, when the determined recirculation canbe associated with group (1), for example, a signal can be output whichis indicative of a correct connection of the extracorporeal bloodcircuit to the vessel and/or, when the determined recirculation can beassociated with group (3), a signal can be output which is indicative ofa swapping over of the arterial and venous connections.

In an embodiment, the evaluation and control unit is configured suchthat, when the determined recirculation has been associated with group(2), the conveying performance of the blood pump is reduced and thecarrying out of steps (a1) and (b) is repeated.

In an embodiment, the evaluation and control unit is configured tooutput a warning signal when the determined blood flow in thecorresponding blood vessel exceeds an upper threshold vale or fallsbelow a lower threshold value.

In this case, a check of the value determined in accordance with theinvention by swapping over the arterial and venous needles and a use ofan already known method can be indicated. The lower threshold value can,for example be 300 or 500 ml/min; and the upper threshold value can, forexample, be 2000 or 1500 ml/min.

The evaluation and control unit can preferably initiate interventions inthe dialysis device required for the data collection (e.g. operation ofthe blood pump at a specific rate or administration of a temperaturebolus). It can be configured such that the determined data orconclusions (e.g. the blood flow in the respective vessel, correct orinverse connection of the needle, signals with respect to a correctaccess, etc.) are automatically used to control the device.

In an embodiment, the blood treatment device has an acoustic and/orvisual output unit by which the data or conclusions (see above)determined by the evaluation unit are output to a user.

The invention furthermore comprises a method of determining the bloodflow in a blood vessel of a patient connected to the extracorporealblood circuit of a blood treatment device, preferably a blood treatmentdevice in accordance with the invention. Provision is made in thisrespect to determine the recirculation in the vessel and to determinethe blood flow in the respective blood vessel of the patient using thisrecirculation and a value for the cardiac output likewise determined orestimated in another manner as the basis.

In addition to the initially named object, it is furthermore an objectof the invention to provide a device for extracorporeal blood treatmentwhich allows a determination of the quality of the vessel access.

In this connection, the invention relates to a blood treatment devicehaving an extracorporeal blood circuit which comprises an arterial line,a blood pump, a blood treatment unit and a venous line, wherein thearterial and venous lines can be connected to a blood vessel of apatient, and wherein the blood treatment device has an evaluation andcontrol unit. Provision is made in accordance with the invention thatthe evaluation and control unit is configured to determine the bloodrecirculation in a blood vessel of the patient connected to theextracorporeal blood circuit and to compare the determined recirculationwith critical values likewise determined or predefined and to group iton the basis of the comparison. A grouping of the recirculation valuestherefore takes place here optionally without determining the blood flowin the blood vessel.

The determination of the blood recirculation can in this respect takeplace as described above.

The device can here furthermore also have an output unit whichcommunicates with the evaluation and control unit, wherein the outputunit and the evaluation and control unit are configured to output adifferent signal to the user depending on the group association of thedetermined recirculation. The output can in this respect take place asdescribed above.

Alternatively or in addition to the output to the user, a response ofthe blood treatment device can be initiated.

Three groups can also be distinguished here analog to the firstembodiment of the invention: (1) the determined recirculation is belowthe critical value for a normal connection; (2) the determinedrecirculation is above the critical value for a normal connection, butbelow the critical value for an inverse connection; and (3) thedetermined recirculation is above the critical value for an inverseconnection.

Likewise analog to the first embodiment of the invention, the evaluationand control unit can be configured such that, when the determinedrecirculation has been associated with group (2), the conveyingperformance of the blood pump is reduced and the determination of theblood recirculation is repeated.

Finally, the invention furthermore comprises a method of determining thequality of the vessel access in a blood vessel of a patient connected tothe extracorporeal blood circuit of a blood treatment device, preferablya blood treatment device in accordance with the invention. Provision ismade in this respect to determine the recirculation in the vessel, tocompare the determined recirculation with critical values likewisedetermined or predefined and to group it on the basis of the comparison.

Further details and advantages of the invention result from thefollowing embodiment shown with reference to the Figures. There areshown in the Figures:

FIG. 1: a schematic representation of an embodiment of a dialysis devicein accordance with the invention;

FIG. 2: a plot of critical values determined in accordance with theinvention for the portion of recirculations R_(n) and R_(x) in a normaland inverse needle position in dependence on the cardiac output CO forextracorporeal blood flows of 200, 300 and 400 ml/min;

FIG. 3: a plot of the relative error on the determination in accordancewith the invention of the shunt flow Q_(a) at a blood flow of 300 ml/minfor values of Q_(a) of 400 to 2000 ml/min;

FIG. 4: a plot of the shunt flow Q_(a) in dependence on CO at differentvalues of the recirculation R_(x) in an inverse needle position at anextracorporeal blood flow of 300 ml/min; and

FIG. 5: a plot of the relative error on the determination of the shuntflow Q_(a) with swapped over needles and with an extracorporeal bloodflow of 300 ml/min.

THEORETICAL BACKGROUND

The algorithm stored in the control unit of the dialysis device inaccordance with the invention in accordance with the embodiment is basedon the theoretical background explained below.

The cardiopulmonary recirculation in hemodialysis patients with acardiac output CO who are treated via a vessel access with a shunt flowQ_(a) is defined as

$\begin{matrix}{{CPR} = \frac{Q_{a}}{CO}} & {{Formula}\mspace{14mu} 1}\end{matrix}$

According to Schneditz (1998), the shunt flow Q_(a) can be determinedwith a known extracorporeal blood flow Q_(b) and a UF rate O_(f) bymeasuring the portion of recirculations R_(n) and R_(x) in a normal andinverse needle position. The following parameters are defined for this.

$\begin{matrix}{{f_{n} = \frac{R_{n}}{1 - R_{n}}},{f_{x} = \frac{R_{x}}{1 - R_{x}}},{\overset{\sim}{Q} = {Q_{b} - Q_{f}}}} & {{Formula}\mspace{14mu} 2}\end{matrix}$

The formula given by Schneditz (1998) herewith reads:

$\begin{matrix}{Q_{a} = {{\frac{1}{f_{x}}\frac{\overset{\sim}{Q}}{1 - {CPR}}{mit}\mspace{14mu} {CPR}} = {\frac{f_{n}}{f_{X}}\frac{\overset{\sim}{Q}}{Q_{b}}}}} & {{Formula}\mspace{14mu} 3}\end{matrix}$

If the cardiac output is known Q_(a) can be calculated with knowledge ofonly one of the values R_(n) or R_(x).

$\begin{matrix}{Q_{a} = {{CO} - \frac{\overset{\sim}{Q}}{f_{n}}}} & {{Formula}\mspace{14mu} 4} \\{Q_{a} = {\frac{CO}{2} - \sqrt{\left( \frac{CO}{2} \right)^{2} - {\frac{{\overset{\sim}{Q}}^{2}}{Q_{b}}\frac{CO}{f_{x}}}}}} & {{Formula}\mspace{14mu} 5}\end{matrix}$

The error of the determination of Q_(a) from CO and R_(n) can beestimated as follows according to the law of error propagation.

$\begin{matrix}{\sigma_{Q_{a}} = \sqrt{\sigma_{CO}^{2} + {\frac{\left( {1 - R_{n}} \right)^{2}}{R_{n}^{2}}\sigma_{\overset{\sim}{Q}}^{2}} + {\left( \frac{\overset{\sim}{Q}}{R_{n}^{2}} \right)^{2}\sigma_{R_{n}}^{2}}}} & {{Formula}\mspace{14mu} 6} \\\; & \; \\{{\sigma_{Q_{a}} = {\frac{1}{2}\sqrt{\begin{matrix}{{\left( {1 - \frac{{\frac{1}{2}{CO}} - \frac{\left( {1 - R_{x}} \right)\overset{\sim}{Q}}{R_{x}}}{W}} \right)^{2}\sigma_{CO}^{2}} +} \\{{\left( \frac{\left( {1 - R_{x}} \right){CO}}{R_{x}W} \right)^{2}\sigma_{\overset{\sim}{Q}}^{2}} + {\left( \frac{\overset{\sim}{Q}{CO}}{R_{x}^{2}W} \right)^{2}\sigma_{R_{x}}^{2}}}\end{matrix}}}}{{{mit}\mspace{14mu} W} = \sqrt{\left( \frac{CO}{2} \right)^{2} - \frac{\overset{\sim}{Q}{CO}}{f_{x}}}}} & {{Formula}\mspace{14mu} 7}\end{matrix}$

It follows from formula 4 or formula 5.

$\begin{matrix}{{R_{n} = \frac{\overset{\sim}{Q}}{\overset{\sim}{Q} + {CO} - Q_{a}}},{R_{x} = \frac{\frac{{\overset{\sim}{Q}}^{2}}{Q_{b}}}{\frac{{\overset{\sim}{Q}}^{2}}{Q_{b}} + Q_{a} - \frac{Q_{a}^{2}}{CO}}}} & {{Formula}\mspace{14mu} 8}\end{matrix}$

Under the physiologically founded assumption that the shunt flow Q_(a)can reach as a maximum 50% of the cardiac output CO, critical valuesresult for R_(n) and R_(x) which cannot be exceeded or fallen below in ameasurement of the recirculation.

$\begin{matrix}{{R_{n,{crit}} = \frac{1}{1 + {\frac{1}{2}\frac{CO}{\overset{\sim}{Q}}}}},{R_{x,{crit}} = \frac{1}{1 + {\frac{1}{4}\frac{Q_{b}}{{\overset{\sim}{Q}}^{2}}{CO}}}}} & {{Formula}\mspace{14mu} 9}\end{matrix}$

The measurement of the shunt flow is desired for various reasons. It isalso important to recognize dangerously high shunt flows (stealsyndrome) in addition to low shunt flows. In accordance with the presentidea, the shunt flow Q_(a) is therefore calculated asQ_(a)=CO−Q_(b)/f_(n), where f_(n)=R_(n)/1−R_(n). R is the recirculationfraction here and Q_(b) the extracorporeal blood flow. The cardiacoutput CO and the recirculation are determined experimentally.Dangerously high shunt flows can thus be recognized without disposableand without any intervention of the user. The concept also manageswithout the introduction of a bolus in one embodiment. With swapped overneedles, a more accurate determination is also conceivable with lowshunt flows due to the higher recirculation.

The determination of the cardiac output can, for example, take placeusing the formula

CO=(MAP−CVP)/R _(P),

where MAP is the mean arterial blood pressure, CVP is the central venouspressure and R_(P) is the peripheral resistance. This method, whichworks according to the principle of “flow=pressure/resistance”, is used,for example, in the commercial available Vicorder devices of the companySMT medical GmbH. The central venous pressure can in this respect, forexample, be measured or estimated using a central venous catheter andcan be input manually and the peripheral resistance can be determinedfrom the falling flank of a pulse curve.

EMBODIMENT

A schematic representation of an embodiment of a dialysis device inaccordance with the invention is shown in FIG. 1.

The dialysis device is generally marked by the reference numeral 1 inthe Figure. It has an extracorporeal blood circuit 2 which comprises ina known manner an arterial line 3 having a blood pump 4, a dialyzer 5and a venous line 6. The arterial line 3 and the venous line 6 areconnected to a vessel 9 of a patient 10 by an arterial needle 7 or by avenous needle 8.

A semipermeable membrane 11 which separates the blood chamber 12 fromthe dialyzing fluid chamber 13 within the dialyzer 5 is arranged withinthe dialyzer 5. The arterial and venous lines 3 and 6 of theextracorporeal blood circuit 2 are connected to the blood chamber 12. Adialyzing fluid system 14 is connected to the dialyzing fluid chamber 13and comprises an apparatus 15 for preparing a dialyzing fluid, a feedline 16 to the dialyzer 5 and an out line 17 from the dialyzer 5. Anultrafiltration pump, not shown in the Figure, can be arranged in theout line 17.

The directions of flow of the blood in the extracorporeal blood circuit2 and of the dialyzing fluid in the dialyzing fluid system 14 are shownby arrows in the Figure.

The dialysis device 1 furthermore comprises an evaluation and controlunit 18 and an output unit 19.

Temperature sensors 20 and 21 respectively are arranged close to therespective needles both at the arterial line 3 and at the venous line 6.

The device 1 furthermore comprises means, not shown in the Figure, forvarying the blood temperature in the venous blood line. These means can,for example, comprise the temperature of the dialyzing fluid produced inthe apparatus 15 being varied according to the demand of the evaluationand control unit 18 with the aim of a change in the blood temperature.Alternatively, the change in the blood temperature can e.g. also takeplace by Peltier elements attached to the blood hose system.

Finally, the device 1 comprises a sensor 22 to measure a pulse pressurecurve progression of the patient which is suitable to determine CO, e.g.by a cuff on the upper arm. The sensor is connected to the control andevaluation unit 18 in a manner not shown in the Figure.

In operation of the apparatus, the blood pump 4 sucks in blood from thevessel 9 of the patient via the arterial needle 7 into the arterial line3 of the extracorporeal blood circuit 2 and subsequently pumps the bloodthrough the dialyzer 5, the venous line 6 and the venous needle 8 backinto the vessel 9 of the patient 10. After administering a temperaturebolus, the temporal temperature progression of the removed and returnedblood is measured at the sensors 20 and 21 and the measured values aretransferred to the evaluation and control unit 18. The recirculation Ris then determined in the evaluation and control unit 18 as described inSchneditz (2003). Furthermore, the cardiac output is determined by meansof oscillometric blood pressure measurements at the blood pressuresensor.

Alternatively, the cardiac output can be estimated with a known strokevolume V_(co) originating, for example, from echocardiogram examinationsor estimated as a typical value of 70 ml, by measuring the heart rate v,by means of CO=v·V_(co).

After determining R and CO and with a known conveying rate of the bloodpump 4 and ultrafiltration rate, the calculations presented above inmore detail are now carried out in the evaluation and control unit 18for determining the blood flow in the vessel 9 of the patient 10. Theresults can, for example, be output at the output unit 19, can betransferred via any desired manner of communication such as via anetwork, and/are can be used automatically for the control of the device1.

Interpretation and Use of the Results:

The results can be interpreted or used in the manner described in thefollowing.

If the cardiac output CO is measured or estimated close in time to themeasurement of the recirculation R, critical values R_(n,crit) andR_(x,crit) for the recirculations R_(n) and R_(x) can be calculated inaccordance with formula 9 in normal and inverse needle positionstogether with the known values for the extracorporeal blood flow and theUF rate, and R can be compared with these values. FIG. 2 shows thecritical values for R_(n) and R_(x) calculated according to formula 9 independence on the cardiac output CO for extracorporeal blood flows of200, 300 and 400 ml/min.

The critical values can, however, also be determined or predefined inanother manner in a further embodiment of the invention.

Different cases can be distinguished which allow different conclusions.

If R<R_(n,crit), only cardiopulmonary recirculation is present. Theshunt flow is therefore larger than the extracorporeal blood flow; thearterial and venous needles are correctly punctured and connected to thehose system. The user can be informed of this in any desired manner bymeans of the output unit 19.

The shunt flow Q_(a) can furthermore be estimated using formula 4. FIG.3 shows the relative error in the determination of Q_(a) calculatedaccording to formula 6 with a blood flow of 300 ml/min under theassumption of an error in the recirculation measurement of ±1% and thedetermination of CO and of Q_(b) of ±10% for values of Q_(a) of 400 to2000 ml/min. It becomes clear from this that the measurement accuracy isvery restricted with low Q_(a) values. It is nevertheless ensured thatQ_(a)>Q_(b) in every case. Since the relative error for high shunt flowsfalls, the determination of Q_(a) can be used to be able to recognizedangerously high shunt flows. Shunt flows>2000 ml/min put a strain onthe heart of the patient, which results in increased mortality. At thesame time, they result in a lack of circulation of the limbs distal ofthe vessel access (typically close to the wrist), i.e. in particular ofthe hand and fingers, which can result in damage to them and inimpairments of the patient. A warning of too high a shunt flow cantherefore be generated on the basis of a shunt flow determined fromR_(n) and CO. If too low a shunt flow of <600 ml/min or too high a shuntflow is detected using the described method, the user can be promptednow to swap over the needles for a more accurate determination of theshunt flow, which is advantageously then easily possible if a disposableis already present for this purpose. Q_(a) can then be determined moreaccurately in accordance with formula 3 from the determination of R_(x);the determination of R_(n) and CO would then only serve aspre-screening.

If R>R_(x,crit), the vessel recirculation is so high that a swappingover of the arterial and venous needles is likely with a highprobability. The user can also be informed of this in any desired mannerby means of the output unit 19.

FIG. 4 shows a plot of the shunt flow Q_(a) in dependence on CO atdifferent values of R_(x) in accordance with formula 5 with anextracorporeal blood flow of 300 ml/min. It can be recognized from thisthat the shunt flow can be determined solely from the measuredrecirculation R_(x) with swapped over needles, in particular at lowshunt flows (<800 ml/min) and that the value of the CO only slightlyinfluences the value of the shunt flow when Q_(a)<¼ CO. This can also berecognized in FIG. 5 where the relative error in the determination ofQ_(a) in accordance with formula 7 was plotted with an extracorporealblood flow of 300 ml/min. The shunt flow can thus be determined solelyby measurement of the recirculation with swapped over needles with onlyan imprecise knowledge of CO without requiring a recirculationmeasurement in a normal needle orientation. The time required fordetermining the shunt flow can thus be considerably reduced. The needleswapping generally has to take place manually by the user while using acorresponding disposable. In the event of an already incorrectly presentneedle swapping, the shunt flow can immediately be given by means offormula 5 once a needle swap has been recognized from the measurement ofthe recirculation and of the CO.

If R_(n,crit)<R<R_(x,crit), there is a partial recirculation between thearterial and the venous needle, which can arise due to an unfavorablepositioning of the needles (e.g. too close to one another).Alternatively, the extracorporeal blood flow can exceed the shunt flow.Provision can be made that the evaluation and control unit 18 isconfigured for distinguishing these two scenarios such that arecirculation measurement is carried out automatically with a reducedblood flow Q_(b)′ and the values are determined again. If the value R′then determined is below R′_(n,crit), Q_(a) is between Q_(b)′ and Q_(b).

It results in summary that the present invention provides a possibilityof recognizing a shunt flow which is above all excessively high. A veryhigh shunt flow is medically undesirable. In accordance with theinvention, the recirculation is determined, for example, byadministering a temperature bolus and the cardiac output is determined,for example, by an oscillometric blood pressure measurement. The shuntflow is calculated from both using formula 4. Said shunt flow can aboveall be determined with a relatively small error at very high flows. Theinvention furthermore allows the determination of two limit values ofthe recirculation and the derivation of corresponding conclusions. Afurther aspect of the invention in particular deals with the comparisonof the recirculation with limit values and with the derivation ofconclusions in isolation from how the limit values are determined.

1. A blood treatment device having an extracorporeal blood circuit whichcomprises an arterial line, a blood pump, a blood treatment unit and avenous line, wherein the arterial and venous lines can be connected to ablood vessel of a patient, and wherein the blood treatment device has anevaluation and control unit, characterized in that the evaluation andcontrol unit is configured to carry out the following steps: (a1)determining the blood recirculation in a blood vessel of the patientconnected to the extracorporeal blood circuit; and (b) calculating theblood flow in the blood vessel using the blood recirculation determinedin accordance with (a1) and using a provided value or a value likewisepreviously determined for the cardiac output of the patient.
 2. A bloodtreatment device in accordance with claim 1, characterized in that theblood treatment device furthermore has a blood pressure sensor; and inthat the evaluation and control unit is configured furthermore to carryout the following step: (a2) determining the cardiac output of thepatient by evaluating the time progression of a pressure pulse measuredusing the blood pressure sensor.
 3. A blood treatment device inaccordance with claim 1, characterized in that the blood treatmentdevice furthermore has a bolus sensor arranged in the arterial line ofthe extracorporeal blood circuit; and in that the evaluation and controlunit is configured to carry out step (a1) in the following manner: (a1)determining the blood recirculation in a blood vessel of the patientconnected to the extracorporeal blood circuit using the signal of thebolus sensor.
 4. A blood treatment device in accordance with claim 1,characterized in that the evaluation and control unit is configuredfurthermore to take account of the extracorporeal blood flow and theoutflow of fluid in the blood treatment device, in addition to the bloodrecirculation and the cardiac output, when determining the blood flow instep (b).
 5. A blood treatment device in accordance with claim 1,characterized in that the evaluation and control unit is configured todefine critical values for the recirculation for a normal and/or inverseconnection of the arterial and venous lines to the blood vessel underthe assumption that the blood flow in the corresponding vessel canachieve a specific portion of the cardiac output as a maximum.
 6. Ablood treatment device in accordance with claim 5, characterized in thatthe evaluation and control unit is configured to compare the determinedrecirculation with these critical values and to group it on the basis ofthe comparison.
 7. A blood treatment device in accordance with claim 6,characterized in that the device furthermore has an output unit whichcommunicates with the evaluation and control unit, wherein the outputunit and the evaluation and control unit are configured to output adifferent signal to the user depending on the group association of thedetermined recirculation.
 8. A blood treatment device in accordance withclaim 6, characterized in that three groups are distinguished: (1) thedetermined recirculation is below the critical values for a normalconnection; (2) the determined recirculation is above the critical valuefor a normal connection, but below the critical value for an inverseconnection; and (3) the determined recirculation is above the criticalvalue for an inverse connection.
 9. A blood treatment device inaccordance with claim 8, characterized in that the evaluation andcontrol unit is configured such that, when the determined recirculationhas been associated with group (2), the conveying performance of theblood pump is reduced and the carrying out of steps (a1) and (b) isrepeated.
 10. A blood treatment device in accordance with claim 1,characterized in that the evaluation and control unit is configured tooutput a warning signal when the determined blood flow in the respectivevessel exceeds an upper threshold value or falls below a lower thresholdvalue.
 11. A blood treatment device having an extracorporeal bloodcircuit which comprises an arterial line, a blood pump, a bloodtreatment unit and a venous line, wherein the arterial and venous linescan be connected to a blood vessel of a patient, and wherein the bloodtreatment device has an evaluation and control unit, characterized inthat the evaluation and control unit is configured to determine theblood recirculation in a blood vessel of the patient connected to theextracorporeal blood circuit and to compare the determined recirculationwith critical values likewise determined or predefined and to group iton the basis of the comparison.
 12. A blood treatment device inaccordance with claim 11, characterized in that the blood treatmentdevice furthermore has a bolus sensor arranged in the arterial line ofthe extracorporeal blood circuit; and in that the evaluation and controlunit is configured to determine the blood recirculation while using thesignal of the bolus sensor.
 13. A blood treatment device in accordancewith claim 11, characterized in that the device furthermore has anoutput unit which communicates with the evaluation and control unit,wherein the output unit and the evaluation and control unit areconfigured to output a different signal to the user depending on thegroup association of the determined recirculation.
 14. A blood treatmentdevice in accordance with claim 11, characterized in that three groupsare distinguished: (1) the determined recirculation is below thecritical value for a normal connection; (2) the determined recirculationis above the critical value for a normal connection, but below thecritical value for an inverse connection; and (3) the determinedrecirculation is above the critical value for an inverse connection. 15.A blood treatment device in accordance with claim 14, characterized inthat the evaluation and control unit is configured such that, when thedetermined recirculation has been associated with group (2), theconveying performance of the blood pump is reduced and the determinationof the blood recirculation is repeated.